Filaments of regenerated cellulose



June 11, 1968 R. ROBERTS ET Al.

FILAMENTS OF REGENERATED CELLULOSE Filed March 26, 1964 /NVEA/O/PS Rober! I Mar/in Ropa/d Rober/s CAUSTIC SODA CONCENTRATION ('/o BY WEIGHT) W/l//am CR/chardson By their afforneys United States Patent O 3,388,117 FILAMENTS F REGENERATED CELLULOSE Ronald Roberts, Mobile, Robert T. Martin, Citronelle, and William C. Richardson, Mobile, Ala., assignors to Courtaulds North America Inc., New York, N.Y., a corporation of Alabama Filed Mar. 26, 1964, Ser. No. 354,975 Claims priority, application Great Britain, Mar. 28, 1963, 12,261/ 63 14 Claims. (Cl. 260-212) ABSTRACT 0F THE DISCLOSURE Regenerated cellulose filaments having conditioned tenacities over 9.5 grams per denier are disclosed together with a modification of the viscose process by means of which such filaments may be made. The process requires spinning viscose having a relatively high gamma number, a viscosity of at least 120 poise and an NaOH/ cellulose ratio of at least l, into a coagulating bath containing formaldehyde, followed by stretching by at least 500% prior to regeneration.

This invention relates to a new and improved class of regenerated cellulose filaments and to a method for making such filaments.

Within recent years fibers of synthetic polymers such as nylon, polyesters, acrylics and polyolefins have replaced natural iibers such vas cotton and wool in many uses. Regenerated cellulose fibers have also been found suitable for a. large number of purposes but the extent to which regenerated cellulose bers have been employed has been limited to a considerable extent by their low tenacity (compared to, say, nylon) and in particular by their low wet strength.

There has recently appeared on the market a group of regenerated cellulose fibers sometimes referred to as high wet modulus or polynosique fibers which are characterized by a fine and stable microfibrillar structure, a minimum wet strength of 2.2 g./ denier and a wet elonga tion of less than 3.5% at a stress of 0.5 g./denier. The manufacture of such fibers is described, for example, in U.S. Patent 2,732,279 to Tachikawa. Normally fibers of this type, 'as marketed, have a conditioned tenacity in the vicinity of g./denier, though in Cox U.S. Patent 2,937,- 070 reference is made to dry tenacities as high as 8 g./ denier. Fibers having dry tenacities as high as 8 g./ denier have not, however, been generally available, and in point of fact, even Coxs patent does not specifically describe such fibers. In `any case, such tenacities are not as high as those currently available in nylon which range up to about 9 g./ denier.

We have now discovered a new type of rayon filament having conditioned (65% relative humidity at 25 C.) tenacities not less than 9.5 g./ denier and on occasion ranging to ll g./ denier or even higher. Wet tenacities are at least 0.75 times the dry tenacities and often 0.8 to 0.9 times the dry tenacities. Such filaments are further characterized by an extraordinary degree of orientation. This is refiectetl in their birefringence ratio which is at least 0.053, and normally 0055-0057.1 by way of comparison, it may be pointed out that conventional textile grade rayon has a birefringence of about 0.022. Various polynosique or high wet modulus fibers currently on the market range from 0.035 to 0.042. P. H. Hermans classic treatise Physics and Chemistry of Cellulose Fibers, Elsevier, Amsterdam, 1949, p. 237, gives an idealized maximum birefringence of 0.043 for a conditioned viscose rayon ber.

1As measured by the technique described in ice For many years it was considered that high crystallinity, as measured by X-ray techniques, was a necessary concomitant of high fiber strength (tenacity). Recently it has become clear, however, that crystallinity is a relative term and while a series of measurements made by the same worker under identical conditions on various fibers, will provide values indicating a scale of crystallinities which is valid enough in a relative way, significant absolute values are not obtainable. In yany case the remarkable tensile properties of the fibers according to the present invention are clearly not associated with a high degree of crystallinity, because while the degree of orientation, is, as indicated above, higher than that of any known regenerated cellulose fiber, the crystallinity of the novel fibers is relatively low, being of the order of 45% on a scale in which conventional textile grade rayon is 42% and Fortisan, a fiber made by the saponification of cellulose acetate, is 51%.

It is implicit in their very high ratio of wet to dry tenacities that fibers made in accordance with the invention are highly inaccessible. This implication is supported by various other measurements. For example, the D20 exchange technique described by Smith, Kitchen and Mutton (Journal of Polymer Science part C, No. 2, pp. 499- 513, 1963) indicates that over and generally over 69% of the fiber is inaccessible. This compares to values of about 42% for commercial textile rayon, 50% for a commercial high wet modulus fiber, 57% for Fortisan and 59% for cotton. High inaccessibility is also indicated by the moisture regain of the novel fiber which is less than 10% compared to l3l4% for conventional tire cord, ll-l3% for high wet modulus bers and 10S-11% for Fortisan. A further characteristic of the novel fiber, related to the concept of inaccessibility, is its behavior toward caustic soda solutions of up to mercerizing strength. When conventional types of regenerated cellulose fibers including tire cord, Fertisan and fibers made according to Cox (U.S. Patent Specification No. 2,937,070), are impregnated with varying concentrations of aqueous caustic soda at 25 C., including the mercerizing range (say 0-20% NaOH), stretched to rupture, and the work product (tenacityxelongation) plotted against caustic concentration, all known fibers show a work product minimum, i.e., there is some value of caustic concentration at which the work product reaches a minimum. This is not the case with the fibers of the present invention which show no substantial variation in wet work product with changing caustic concentration at 25 C.

From the foregoing it will be seen that fibers according to the invention are characterized by an exceedingly high tenacity, a high degree of orientation as indicated `by their birefringence and a high degree of inaccessibility. The physical structure defined by these objectively determined parameters is, of course, not necessarily subject to description in familiar terms and we do not wish to be bound by any particular structural theory in explanation of the extraordinary physical properties of our new fibers. `On the other hand, it is sometimes useful to the understanding of a new polymer structure to picture it in cornmonplace terms. Bearing in mind the limitations of such models, one may think of the cellulose molecules as chains having a longitudinal axis and different surface characteristics around their circumference and along their length. Those molecules, or perhaps those portions of molecules which form part of a crystal, must not only have their axes aligned with the axes of the other molecules in the crystal, but each must -be properly rotated about its own axis and must have suitable regions along its length paired with compatible regions of adjacent molecules. On the other hand, for a fiber to be highly oriented it is only necessary that the axes of the molecules closely approach parallelism with the axis of the fiber.

assaut For a fiber to be inaccessible it is necessary that the adjacent .molecules be closely packed laterally.

The picture of the novel fibers which then emerges, is one in which the cellulose molecules are laid substantially parallel to, though not necessarily matched along their length with, adjacent molecules and aligned with the liber axis; and in which the molecules are very closely associated laterally. This close lateral association can be inferred not only from the low accessibility of the fibers, but also from the lack of a diffuse background in X-ray photographs. Further, the very Ihigh moduli in both the wet and the dry states also indicate the close alignment of the molecules in the direction of the fiber axis.

The drawing is a graph comparing the effect of caustic soda on fibers according to the invention with the effect on prior art fibers.

In making fibers according to the invention, viscose having a gamma value of more than 80, a viscosity of at least 120 poise and a NaOH/cellulose ratio of at least 1, is spun into a coagulating bath having a temperature of at most 30 C. and containing from about 3% to about 8% sulfuric acid, from zero to say 12% Na2SO4 and between about 0.3 and about 1.5% formaldehyde, to form filaments. The filaments are then stretched by at least 500%, the stretching being commenced when the filaments have a gamma value of at least 60, and at least a part of the stretching taking place when the laments are in contact with water at a temperature greater than 80 C.

The cellulose used in the present process may have a high degree of polymerization (say 800-1500) but this is not critical and high performance fibers have been obtained with conventional pulps, having lower D.PS. The cellulose is converted to alkali cellulose in conventional manner. Normally between about 2000 and about 3000 parts of a caustic soda liquor having a concentration of say 18 to 21% NaOH is used per 100 parts of cellulose. Steeping is carried out at say 16 to 25 C. for 20 to 60 minutes. The press weight ratio is conventionally 2.2 to 2.8. Preferably there is added to the steep liquor a sequestering agent capable, under alkaline (pHlO) conditions, of chelating polyvalent cations such as calcium, magnesium and iron, present as trace impurities in the pulp or liquor. Such agents are commonly available on the open market. A particularly useful group includes the alkali metal and especially the sodium salts of amino carboxylic acids such as imino diacetic acid (IDA), nitrilotriacetic acid (NTA) and ethylenediamine tetraacetic acid (EDTA). The sequestering agent is normally used in a proportion of 0.02 to 2 parts by weight per 100 parts of tat-cellulose. As will appear below, a portion of this may be added to the dissolving soda.

The resulting alkali cellulose is shredded at say 16 to 24 C. for say .5 to 1.5 hours and is charged with or without aging (say to 30 hours) to a Xanthating vessel.

Xanthation is preferably conducted at constant temperature, or as close to constant temperature as possible, in the range of say 18-32" C. under conditions which avoid localized heating` This can be achieved by thorough mixing of the alkali crumbs with the carbon disulde, but inadequate mixing can be compensated for by adding the carbon disulfide in two or more increments and allowing sufcient time between each addition for the mixture to react. .In this way, the amount of free liquid carbon disulfide in the reaction vessel at any time is restricted.

As noted earlier, the gamma number of the viscose at spinning is above 80. Preferably it is above 100, say 100 to 115. The amount of CS2 added will be say 1.33 to 1.05 times the equivalent amount.

When Xanthation is completed, the Xanthate crumbs are dissolved and the resulting viscose is preferably kept cool, for example below C., from the time it is iirst made until it is spun. This may be accomplished by adding the Xanthate to dilute, (1.5 to 4% NaOH) caustic at -5 to 5 C. and maintaining some refrigeration during the mixing process so that the temperature does not rise above about 10 C. The dissolving liquor may contain a sequestering agent of the type indicated above, the total amount of combined agent used in both the steep liquor and the dissolving liquor, being in the range 0.02 to 2 parts/100 parts of nt-cellulose. Additional carbon disulfide, say 2 to 10% on cellulose may be added to the dissolver or subsequently, if desired.

In general, it is found that viscoses made in the manner discussed above are paler than if the carbon disulfide is added in a single batch and if adequate cooling is not provided. Analysis of the viscose for total sulfur content and sulfur present in Xanthate groups, shows that a high proportion is present as Xanthate.

The properties of the viscose are not impaired by storage before or after deaeration so long as the gamma number does not decay to below at the time the viscose is spun.

As noted above, the viscose must have a gamma number above S0 at spinning, and preferably above 100. Normally, the gamma number will range from say to 105. The viscosity at spinning will be at least poiscs, preferably between about and about 600 poises. The viscose will preferably contain between 3.5 and 6% cellulose, with an NaOH/cellulose ratio of at least 1 and usually between about 1.1 and about 1.6. We have found that fibres having tenacities of 10 g.p.d. and higher are made more consistently when the viscosity of the viscose is high and within the range 150 to 600 poises.

The viscose is spun at a spinning speed of say 25 to 70 metres/minute into a coagulating bath relatively low in regenerative power, containing by weight, between about 3% and about 8%, preferably between about 4 and about 6% H2804 and between about 0 and about 12%, preferably not more than 5%, Na2SO4. It will be understood that there will always be some Na2SO4 in the bath from neutralization of the viscose caustic soda` The spin bath also contains between about 0.3 and about 1.5% formaldehyde.

When the lilaments have been in the spin bath long enough to acquire sufiicient strength, they are stretched by at least 500%, and preferably by between about 550% and about 850%. At this stage the gamma number must be not less than 60 and is preferably 615 to 90. The

filaments may be stretched in the coagulating bath or in air, but are preferably stretched in a secondary bath of hot (80 C.100 C.) water. This bath may contain up to say 4% H280., but is preferably substantially neutral, containing less than 0.1% H2502. See Klein Patent 3,109,698.

Regeneration will normally be accomplished during stretching. However, if necessary, the .laments can be contacted with a final bath of hot water or hot dilute acid to complete the regeneration.

Following regeneration the filaments may be given the usual desulfurization, souring, washing and drying treatments conventional in the art. They may be cut up to form staple either immediately after regeneration or subsequently, if it is desired to produce staple fiber.

The invention will be further described with reference to the following specific examples which are given for purposes of illustration only. They are not to be taken as in any way limiting the invention beyond the scope of the appended claims.

Examples 1 to 8 vIn Examples 1 to 8 the alkali cellulose was prepared by steeping a high B.P. pulp for 30 minutes in 20% NaOH at 20 C. The steep liquor contained 0.01% Sequestrene NA-4 (EDTA). The press-weight ratio was 2.70i0-05. The alkali cellulose was shredded for 1 hour at 18 C. in a Blaschke pfleiderer and, without aging, was Xanthated. Xanthation was carried out in two stages, or in a single stage, as specified in Table I below. 1n carrying out two stage Xanthation the pressure in the xanthation churn was measured. When the pressure drop indicated that a .major portion of CS2 had been reacted, a second washed and dried. They had a conditioned tenacity of 9.92 g./denier and a conditioned elongation of 7.1%, a wet tenacity of 8.53 g./denier and a wet elongation of 8.5%. Their Ibirefringence was measured at 0.0576.

These filaments were then compared with Fortisan, lilaments made according to Cox 2,937,070 (Example l1) and a commercially available polynosique fiber for the behavior in caustic soda. Specifically, samples of each ber were let stand in caustic soda of varying concentrations at room temperature and immediately drawn while still wet, in an Instron tester to break. The work product TABLE I VISCOSE MANUFACTURE Xanthation Dissolving Viscose Example No. No. Percent CS2 T., Time Percent CS2 T., Percent Percent Percent Percent Stages on Cell C. Hrs. Min. on Cell C. Cell NaOH Total S Xant. S

TABLE II.-SPINNING Viscose Spin Bath Example No. Viscosity Gamma Viscose temp., Stretch, (poises) Number Age, Hrs. C. Percent Percent Percent Temp., percent HzSOi NazSOi HCHO C.

TABLE ITL-PHYSICAL PROPERTIES Dry l Dry f Wet Wet Wet Tenacity Dry Initial Wet Initial Example No. Denier Tenacity Elongation Tenacity Elongation Modulus Modulus Dry Tenacity (md/100% (g./d./100% extension) extension) 1. 01 10. 40 7. 2 8. 30 8. 4 0. 80 0. 89 10.07 7.0 8. 76 8.0 0.82 95 1g. g. g Z6 1 0. 80 11 1 1 5 0. 86 1.03 10. 7. 9 9. oi s. 6 o. ss 2 28H20 2 70100 0. 88 10.11 7. 5 8. 86 8. 5 0.88 1. 07 9. 72 7. 4 8. 50 8.6 0. 87 0. 03 10.00 7. 5 S. 04 7. 6 0.80

1 The dry tenacity and elongation are measured at 65% from to 60 grams/denier/100% extension.

Example 9 The general procedure of Examples 1-8 was carried out to make an additional sample. In this specific instance a two stage xanthation was employed with 35% CS2 based on cellulose, added in each stage. The xanthation temperature was 22 C. and the time 4 hours 10 minutes. Approximately 4% CS2 was added to the dissolver which was kept rat 8 C. The viscose contained 4.86% cellulose, and 6.78% soda. lt was spun after four hours at a gamma number of 113.4, a temperature of 7 C. and a viscosity of 426 poises. The spinning bath contained 4.53% H2504, 1.47% HCHO and around 1% Na2SO4. Its temperature was 22 C. The laments were stretched 841% in hot water, washed and dried. They had a conditioned tenacity of 10.60 g./denier.

Samples of this ber were then tested for inaccessibility by the D20 exchange technique described by Smith et al., cited above. A value of 69% was obtained.

Example 10 Another sample was prepared using the general technique of Examples 1-8. Specifically a viscose containing 4.48% cellulose and 6.75% NaOH was spun at a gamma number of 99.3 and a viscosity of 388 poises into a bath containing 5.20% H2504, 0.77% formaldehyde and about 1% Na2SO4 and having a temperature of about 28 C. The iilarnents were stretched 578% in water at 95 C.,

l relative humidity. The values are average values. 2 Fortisan in tite same tests has a dry initial modulus of from 180-220 grams/denier/l00% extension and a wet initial modulus oi TABLE IV Work Product Percent NaOH This invention Fortisan Cox H.W.M.

72. 5 40. 7 54.8 56. 8 70. 3 38.0 43. 7 44. 8 74. 9 50.0 4i. 4 55. 4 77. 1 30. 7 60. 1 24. 5 67. 1 39. 3 27. 6 0 69. 5 21. 1 10. 2 0 91. 4 30. 0 44. 3 16. 53 7G. 5 36. 3 50.0 61.0 68. 4 38. 0 5l. 1 42. 1 70.1 47. 3 59.8 76. 8

What we claim is:

1. Regenerated cellulose filaments having a conditioned tenacity above about 9.5 g./ denier, a Wet tenacity at least 0.75 times the conditioned tenacity and a conditioned birefringence of at least 0.053.

2. Cellulose filaments characterized by a conditioned tenacity of at least 9.5/ denier, a conditioned birefringence of at least 0.053 and a D20 inaccessibility of at least 65%.

3. Regenerated cellulose filaments whose wet work product is substantially unaffected when impregnated with aqueous solutions containing to 20% NaOH at 25 C.

4. Regenerated cellulose filaments having a conditioned tenacity of at least g./denier, a wet tenacity of at least 8 g./denier and a. conditioned biretringence of at least 0.053.

5. Regenerated cellulose filaments having a conditioned tenacity of at least 9.5 g./denier, a conditioned bircringence of at least 0.053 and whose wet work product is substantially unatlected when impregnated with aqueous solutions containing from 0 to 20% NaOH at 25 C.

6. A method for making high tenacity regenerated cellulose tlamentary material which comprises extruding viscose having a ,gamma number greater than 80, viscosity of at least 120 poises and a NaOH/cellulose ratio of at least 1 into a coagulating bath having a temperature not greater than C. and containing between about 3% and about 8% H2804, between 0 and about 12% Na2SO4 and from 0.3 to 1.5% HCI-IO to form filaments, stretching the filaments by at least 500%, and then completing the regeneration of said filaments.

7. The method claimed in claim 6 wherein the filaments are stretched in contact with water at a temperature of at least C. and the stretching is begun before the gamma value of the filaments has fallen below 60.

8. A method for making high tenacity regenerated cellulose filamcntary material which comprises reacting cellulose with sodium hydroxide to form alkali cellulose, Xanthating the alkali cellulose to form sodium cellulose Xanthate dissolving the cellulose Xanthate to form viscose having a NaOH/cellulose ratio of at least .1, a viscosity of at least poises and a gamma number greater than 80, spinning said viscose into a coagulating bath low in regenerative power and containing formaldehyde to form filaments, removing the filaments from the coagulating bath While their gamma number' is not less than 60, and

8 stretching the filaments by at least 500% while they are in contact with hot water.

9. The method claimed in claim 8 wherein the xanthation is carried out in a plurality of stages.

10. The method claimed in claim 8 wherein the viscose contains 0.02 to 2% based on cellulose of a sequestering agent capable of chelating polyvalent cations in alkaline solution.

11. The method claimed in claim 10 wherein the sequestering agent is added, at least in part, during the formation of the alkali cellulose.

12. The method claimed in claim 10 wherein the sequestering agent is added in part during the dissolving of the cellulose xanthate.

13. The method claimed in claim 8 wherein the viscose is kept cold from the time it is formed until it is spun.

14. The method claimed in claim 13 wherein the viscose is kept below 10 C. from the time it is formed until it is spun.

References Cited UNITED STATES PATENTS 2,933,475 4/1960 Hoover et al 106-194 X 3,038,780 6/1962 Kiefer etal 106-165 X 3,079,213 2/1963 Mendelsohn et al. 260-91.3 X 3,107,970 10/1963 Kusunese et al. 264-197 3,226,461 12/1965 Wise et al. 264-198 X 2,663,704 12/1953 Yehling 260-217 2,847,272 8/1958 Edwards 264-192 3,337,671 8/1967 Dresch et al. 264-195 X FOREIGN PATENTS 590,660 1/1960 Canada.

JAMES A. SEIDLECK, Primary Examiner.

ALEXANDER H. BRODMERKEL, Examiner.

I. H. WOO, Assistant Examiner. 

